Munster prop James Cronin and hooker Rhys Marshall are out of the Guinness Pro14 trip to Benetton Treviso on Saturday evening.
The pair both picked up knee injuries during the narrow defeat to Leinster at Thomond Park on Saturday night.
In more positive news, Joey Carbery is continuing to make progress in his recovery from an ankle injury. The outhalf took part in some elements of training on Tuesday, with Munster saying the next stage of his rehab will see him "manage his training load".
The 25-year-old hasn't played since he suffered a wrist injury in a Pro14 clash against Ulster on 3 January 2020. A recurring ankle problem has kept him sidelined for over a year.
"In the last month or so I have tried to jump in with the backs as much as possible [in training]," Carbery said last week.
"It makes it a bit easier when you're in a team environment, getting to the meetings and just being in with the squad makes a huge difference mentally. It is the only thing that has really got me through this, looking to the end and wanting to be back on the pitch."
Meanwhile, hooker John Andrew, lock Kieran Treadwell, prop Andrew Warwick and 19-year-old scrum-half Nathan Doak have all signed new two-year deals with Ulster.
Treadwell, 25, has made 99 appearances for the province and won three Ireland caps.